Overhead cranes typically include a pair of runways, which may be mounted fixedly to the roof joists of an industrial plant, a bridge that includes one or more bridge rails which have rollers at their ends for rolling along the runway rails, and a trolley which has rollers thereon for rolling along the one or more bridge rails. A hoist or some other lifting device is provided on the trolley for lifting a load.
For cranes having capacities of more than 4000 pounds, I-beam crane rails are typically used for the one or more bridge rails and for the runways. For cranes having capacities of less 4000 pounds, enclosed track crane rails, such as the crane rail shown at 100 in FIG. 1 are typically used.
A particular category of cranes is referred to as ‘light’ cranes, and typically have a capacity of about 2000 pounds or less. Light cranes typically do not have tractor drives on the bridge and trolley, which means that the load, once lifted off the plant floor, is moved around manually by the crane operator.
For such cranes, the weight of the bridge rails directly impacts the effort that the operator is required to exert when moving the lifted load to its destination. It is thus generally desirable to reduce the weight of the bridge rails. By reducing their weight, the effort required to move a given size of lifted load can be reduced.
A typical enclosed bridge rail is shown in FIG. 1. One method that has been used to reduce the weight of the bridge rail is to manufacture the bridge rail out of aluminum.
Another way has been disclosed in U.S. Pat. No. 8,960,459 issued on Feb. 25, 2015 to Givens.
It would be desirable to find other ways of reducing the weight of the bridge rail while reducing the possibility that the bridge rail may twist when loaded, particularly for light cranes that lack tractor drives for moving the bridge on the runways.